(a) Field of the Invention
The present invention relates to a circuit and method for a motor control. More specifically, the present invention relates to a circuit and method for a brake control of a spindle motor.
(b) Description of the Related Art
Spindle motors are used to drive compact disc read only memories (CD-ROMs), digital video disks (DVDs) and video cassette recorders (VCRs), and a brushless direct current (BLDC) motor is the main mode of spindle motor in use.
A motor converts electrical energy into mechanical energy, and the rotation speed and rotation direction of the motor depend on the strength and direction of the current supplied to the motor. Conventionally, a motor driving circuit includes an inverter for controlling the strength and direction of the current supplied to the motor, and the inverter includes a plurality of switches.
Switching sequences of a switch of the inverter in the conventional BLDC motor are adjusted with an identical phase of the back electromotive force (BEMF) supplied to the motor so as to rotate the motor in the forward direction (will be referred to as a forward rotation hereinafter), and the speed of the motor is controlled by controlling the current flowing to each switch (i.e., the current flowing to the motor).
On the other hand, when it is necessary to stop the motor from moving in the forward rotation at the desire of a user, a method for stopping the motor is referred to as a brake method.
Brake methods of the conventional spindle motor are categorized as a mechanical brake method and an electrical brake method.
The mechanical brake method is such that when the user wants to brake the spindle motor, all the switches of the inverter are switched off so as to stop the supply of electrical energy. Since the motor exhausts the current energy as friction energy according to the mechanical brake method, the motor finally stops. However, when using this method, the time it takes to stop the motor is significant, and therefore this method can only be applied to systems in which the time it takes to stop the motor is not important.
Examples of the conventionally used electrical brake method are categorized as a reverse brake method that controls the switching sequences of the switch so the current in the motor flows in a phase opposite to the BEMF supplied when the motor is moving in the forward rotation; and a short brake method that turns off an upper switch (i.e., the switch for supplying the motor with the current from the voltage) of the inverter and turns on a lower switch (i.e., the switch for supplying the ground with the current from the motor) of the inverter so as to extinguish the motor energy by using only elements of the lower switch.
The above-noted electrical brake method has a merit of stopping the motor in a shorter time, however it has a deficiency of excess heat generation in the switches of the inverter. This problem of heat generation becomes greater as faster CD-ROMs such as 44xc3x97-speed CD-ROMs appear.
It is an object of the present invention to provide an optimized circuit and method for a motor brake for solving the problems of excess stopping time and heat generation that occur when the user tries to brake the motor.
In one aspect of the present invention, in a method for controlling a motor control circuit comprising an inverter including a first switch unit comprising a plurality of switches coupled between each voltage source and phase of the motor and a second switch unit comprising a plurality of switches coupled between the motor and the ground, and a switching controller controlling onloff operations of each switch of the inverter, the method comprises the steps of: (a) adjusting switching sequences of the switches of the inverter and adjusting direction of the current flowing to the motor in order for the motor to rotate in the forward direction; (b) turning off all the switches of the inverter in order for the rotation speed of the motor to reduce by mechanical frictions; and (c) making, when the reduced speed of the motor is slower than a first speed, the energy supplied to the motor exhaust itself through the switches of the inverter in order to reduce the speed of the motor.
The step (c) is characterized in that all the switches of the first switch unit are turned off and all the switches of the second switch unit are turned on so as to reduce the speed of the motor, and that the switching sequences of the switches of the inverter are adjusted so that the current flows in the opposite direction of the step (a), and therefore, the speed of the motor is reduced.
In another aspect of the present invention, a motor control circuit comprises: an inverter including a first switch unit comprising a plurality of switches coupled between each voltage source and phase of the motor and a second switch unit comprising a plurality of switches coupled between each motor and the ground; a switching controller, that when receiving an acceleration signal from the outside controls the switching sequences of the switches of the inverter in order for the motor to rotate in the forward direction, and when receiving a brake start control signal from the outside, turns off all the switches of the inverter so that the rotation speed of the motor is reduced by the mechanical frictions; and an electrical brake determiner outputting an electrical brake start signal to the switching controller when the rotation speed of the motor is slower than a first speed because of the mechanical friction of the motor, wherein the switching controller, when receiving the electrical brake start signal from the electrical brake determiner, makes the energy supplied to the motor exhaust itself through the switches of the inverter so that the speed of the motor is reduced.
The switching controller, when receiving the electrical brake start signal, turns off all the switches of the first switch unit and turns on all the switches of the second switch unit.
The switching controller, when receiving the electrical brake start signal, controls the switching sequences of the switches of the inverter in order for the current to flow in the direction opposite to the direction of the current when the motor rotates in the forward direction.
The electrical brake determiner comprises: a speed detector detecting the rotation speed of the motor; and a speed comparator comparing the detected rotation speed of the motor with the first speed, and when the rotation speed of the motor is slower than the first speed, outputting the electrical brake start signal to the switching controller.
The speed detector comprises: a comparator comparing a hall signal from a hall sensor with a reference voltage and outputting pulse type signals; and a counter receiving the output signals of the comparator and counting the number of the pulse type signals, and computing the rotation speed of the motor from the counted pulse type signals and counting time.
The speed detector obtains the rotation speed of the motor through information stored in a storage media driven by the motor.